Use the uncached form of BacktraceMap::Create.

The code assumes that calling BacktraceMap::Create creates a map based
on the current state of the maps. This is not true by default, so
call the Create function indicating we want an uncached BacktraceMap object.

(cherry picked from 27a10f61)

Change-Id: Ic7a2dedaea9950174b24ede4dcda30ffe036fe93